1. Field of the Invention
The present invention relates to a cornering power control device and a method for controlling a cornering power of a wheel and, more specifically, to vehicle control under which the kinetic state of a vehicle is controlled through control over the cornering power.
2. Description of the Related Art
A vehicle control technology has been conventionally known for controlling the kinetic state of a vehicle. Exemplarily applied thereto is a technique of controlling a driving/braking torque to be exerted on wheels, or controlling the suspension property of the wheels. With the vehicle control technology, exemplarily in such a driving condition as cornering, the steerbility and stability are improved through optimal control applied to the kinetic state of the vehicle. Such a technology includes a vehicle control device for controlling the kinetic state of the vehicle by using a wheel friction force utilization ration(refer to Japanese Patent No. 3132190 as an example). In this vehicle control device, the wheel friction force utilization ration is derived for each of the wheels, and a wheel state amount of the respective wheels is so controlled that the resulting wheel friction force utilization ratio is brought closer to a target wheel friction force utilization ratio. At this time, the wheel friction force utilization ration is calculated as a ratio of an actual friction force to the maximum friction force. Here, the actual friction force is a resultant force of the longitudinal force and the lateral force actually being generated between the wheels and the road surface. The maximum friction force is the product of the actual friction coefficient between the wheels and the road surface and the vertical force actually being generated between the wheels and the road surface.
To effectively control the kinetic state of the vehicle in a driving condition under which such vehicle control works more effectively, e.g., cornering driving or driving on low-μ roads, inventors, et al. of the present invention consider it preferable to pay attention on the cornering power. The reason is that, in driving stability analysis or vehicle dynamics control using a two-degree-of-freedom vehicle dynamics model (a model having considered translational motion in the lateral direction and rotary motion around a vertical axis), the cornering power is generally used for formulation such as static margin, or stability factor. Moreover, as to the cornering power, the responsivity of the (behavior change) cornering force is depending on the value size thereof. That is, the cornering power is considered as being an important factor for evaluating the steerbility and stability of the vehicle. As an example, in the above conventional technology, the kinetic state of the vehicle is improved by bringing the wheel friction force utilization ratio closer to the target wheel friction force utilization ratio. The problem is that, even if the wheel friction force utilization ratio is brought closer to the target wheel friction force utilization ratio, in view of the cornering power, the cornering power at this time may not be appropriate in value for the wheels. For example, if the cornering power is considerably smaller than the cornering power required for the wheels, there is a possibility that the vehicle controllability will be lost.